A fluid control valve is one that intervenes between an upstream side flow path and a downstream side flow path, to control a flow rate or pressure of fluid flowing through the flow paths, or to fully close to prevent the fluid from flowing between the respective flow paths.
For example, a thermal type mass flow controller that is, sequentially from an upstream side, provided with a thermal type flow rate sensor and such a fluid control valve is used for a semiconductor manufacturing process.
In recent years, the semiconductor manufacturing process has required flow rate control performance having higher accuracy than before, and therefore the thermal type mass flow controller has been sometimes replaced by a pressure type mass flow controller that is provided with a pressure type flow rate sensor having higher measurement accuracy and responsiveness than the thermal type flow rate sensor.
Meanwhile, as described in Patent literature 1 and illustrated in FIG. 8(a), there is one pressure type mass flow controller 100A that is, sequentially from an upstream side, provided with a fluid control valve V, and a first pressure sensor P1, fluid resistor L, and second pressure sensor P2 that constitute a pressure type flow rate sensor FS.
In the case of replacing the above-described thermal type mass flow controller in which the fluid control valve is present on a downstream side of the flow rate sensor by such a pressure type mass flow controller 100A in which the fluid control valve V is provided on the upstream side of the pressure type flow rate sensor FS, a difference in mode of outputting a measured flow rate value from the flow rate sensor FS in the case of bringing the fluid control valve V to a fully closed state may become a problem.
That is, in the case of the above-described configuration of the thermal type mass flow controller, when the fluid control valve is fully closed, a measured flow rate value is substantially simultaneously outputted as zero, whereas in the case of the pressure type mass flow controller 100A having the configuration as illustrated in FIG. 8(a), even when the fluid control valve V is fully closed, a measured flow rate value decreases over a predetermined time and asymptotically approaches zero. In the case where there is a difference in behavior of a measured flow rate value after the fluid control valve V has been fully closed, in the semiconductor manufacturing process that uses a measured flow rate value as a trigger to set up various types of sequences, it is necessary to redo threshold settings and the like, and perform other work, and therefore in some cases, it is not easy to replace a mass flow controller.
The reason why as described, in the mass flow controller 100A having the configuration as illustrated in FIG. 8(a), a phenomenon appears in which even in the case of fully closing the fluid control valve V, the measured flow rate value does not instantaneously reach zero, is because the fluid remaining in the volume from the fluid control valve V to the fluid resistor L at the time of fully closing the fluid control valve V flows toward the downstream side.
Accordingly, by making the volume from the fluid control valve V to the fluid resistor L as small as possible, even in the above-described pressure type mass flow controller 100A, a time necessary for the measured flow rate value to decrease to zero or a value near zero after the fluid control valve V has been fully closed can be shortened, and therefore the pressure type mass flow controller 100A can be made to exhibit substantially the same behavior as that after the fluid control valve of the thermal type mass flow controller has been fully closed.
However, regarding the above-described volume, in particular, it is difficult to miniaturize the fluid control valve V to reduce the volume of the fluid control valve V.
More specifically, as illustrated in FIG. 8(b), the fluid control valve V is that is provided with: a valve seat block 5A; a valve element member 6A; an actuator 3A provided with a piezo stack 31A that drives the valve element member 6A; and a coil spring SP for, in a state where voltage is not applied, restoring the piezo stack 31A to an upper initial position. Also, the valve seat block 5A is, as illustrated in FIG. 9, formed in a substantially cylindrical shape, and provided with: a first in-valve flow path 51a that opens in a bottom surface part 52A and in an upper surface part 53A, and is formed inside of the valve seat block 5A so as to be communicatively connected to an upstream side flow path; an L-shaped second in-valve flow path 51b that opens in the upper surface part 53A and on a bottom part side of an outer circumferential surface 59A, and formed inside of the valve seat block 5A so as to be communicatively connected to a downstream side flow path 23; and an annular-shaped protruded rim 54A that is, in the upper surface part 53A, protruded so as to surround an outflow opening of the first in-valve flow path 51a and an inflow opening of the second in-valve flow path 51b without space, and in an upper part, provided with a pressed surface 55A that is pressed toward the bottom surface 52A side at the time of assembling. As can be seen from two-dotted lines with arrows in FIGS. 8(b) and 9, the fluid flowing from the upstream side flow path 22 flows in the order of the first in-valve flow path 51a, an inner side part of the protruded rim 54A in the upper surface part 53A, the second in-valve flow path 51b, a space between the outer circumferential surface and a body of the mass flow controller, and the downstream side flow path 23.
In the case of attempting to miniaturize the valve seat block 5A having such structure while keeping the same shape, and thereby reduce inside volume, in terms of space, it is difficult to form both of the first in-valve flow path 51a and the second in-valve flow path 51b inside. Also, even in the case of being able to form both of the in-valve flow paths while miniaturizing the valve seat block 5A, under the presence of the two in-valve flow paths, the inside volume cannot be reduced so much, and consequently, it is difficult to, in a short period of time, decrease to zero the measured flow rate value measured by the pressure type mass flow controller 100A after the full closing.